1. Field of the Invention
This invention relates to electrochromic antiglare mirrors hereinafter referred to as EC mirror, which are useful as antiglare mirrors for an automobile.
2. Description of the Prior Art
Electrochromic mirrors have been used for glare-protection purposes from light emanating from the headlights of vehicles approaching from the rear by reversibly varying reflectance to electromagnetic radiation. Demand for such electrochromic mirrors has gone up sharply in recent years.
In general, an electrochromic mirror is formed by a transparent electrically conductive substrate and a reflective electrically conductive substrate between which an ion conductive layer is disposed. As disclosed in Japanese Patent Laid-Open Publication Nos. 9-120088 and 7-70218, there were reported considerably large number of EC mirrors having an ion conductive layer containing organic electrochromic materials such as viologen derivatives. However, these EC mirrors have a problem that coloration continued for a long time would cause the occurrence of remnant at the cathode side, i.e., would not clear immediately after the application of an electric voltage continued for a long time is terminated. Furthermore, an electrochromic mirror with a large size fails to color at its center portion especially at elevated temperatures. In the case of using a reflective electrode substrate having both a reflective layer and an electrode layer, such a reflective electrode substrate has a higher electric conductivity than those of conventional transparent substrates and thus can improve the response capability of the resulting electrochromic mirror. However, it has a malfunction that in the early stage of coloration the coloration of an electrochromic mirror including it biases from the side of a transparent conductive substrate where a lead wire is connected. Larger difference in surface resistance between the transparent conductive substrate and the reflective electrode substrate, this malfunction is more significant.
Therefore, an object of the present invention is to provide an electrochromic mirror which is free from remnant even after a long period of coloration and has an excellent response ability regardless of its size and also free from biased coloration in the early stage even using a reflective electrode substrate which is lower in surface resistance than a transparent conductive substrate.
After an extensive research and development, it was found that an EC mirror exhibiting the above-mentioned excellent performances can be obtained by arranging on the peripheral portions of the electrically conductive surface of at least one of the electrically conductive substrates a highly conductive layer having lower resistance than the surface resistance of the conductive surface.
According to the present invention, there is provided an electrochromic mirror comprising a transparent conductive substrate, a reflective conductive substrate, and an ion conductive layer disposed therebetween wherein at least one of the substrates is provided on the peripheral portions of its conductive surface with a highly conductive layer having a lower resistance than the surface resistance of the conductive surface.
The highly conductive layer is preferably provided at least on the peripheral portions and/or end surfaces of the conductive surface of one of the conductive substrates. The highly conductive layer is preferably provided at least on the peripheral portions of the conductive surface of the transparent conductive substrate. The highly conductive layer is preferably arranged in the form of lines on portions in the vicinity of the periphery of the conductive surface of the substrate. Furthermore, in an electrochromic mirror of the present invention, the pair of the conductive substrates are preferably joined at their peripheries with a sealant such that the highly conductive layer is free from the contact with the ion conductive layer with the aid of the sealant. Moreover, an electrochromic mirror of the present invention has an ion conductive layer containing an electrochromic compound.